SI-Based Class AB Power Amplifier for Wireless Medical Sensor … · 2017-07-04 · SI-Based Class...
Transcript of SI-Based Class AB Power Amplifier for Wireless Medical Sensor … · 2017-07-04 · SI-Based Class...
SI-Based Class AB Power Amplifier for Wireless
Medical Sensor Network
Wei Cai Department of Electrical Engineering and Computer Science, University of California, Irvine, CA, USA
Email: [email protected]
Liang Huang Department of Information & Electronic Engineering, Zhejiang Gongshang University, Hang Zhou, Zhejiang, China
Email: [email protected]
Wujie Wen Department of Electrical and Computer Engineering, Florida International University, Miami, FL, USA
Email: [email protected]
Abstract—The objective of this research was to design a 2.4
GHz class AB Power Amplifier (PA), with 0.18um
Semiconductor Manufacturing International Corporation
(SMIC) CMOS technology by using Cadence software, for
health care applications. The ultimate goal for such
application is to minimize the trade-offs between
performance and cost, and between performance and low
power consumption design. This power amplifier can
transmit 8.5 dBm output power to a 50Ω load. The power
added efficiency is 8.2% at 1dB compression point and the
power gain is 10dB, the total power consumption is 0.15W.
The performance of the power amplifier meets the
specification requirements of the desired.
Index Terms—two stage, class AB, power amplifier
I. INTRODUCTION
Currently, remote monitoring applications are
extremely important mobile technologies, because they
can detect and prevent the illness. Thus, they could
reduce hospital readmission rates, saving hospital
resources. Remote monitoring systems help patients
effectively be aware of their physical conditions, and
commute more efficiently get in touch with their
physicians [1].
Wireless medical sensor networks have offered
significant improvements to the healthcare industry in the
21st century. Devices are arranged on a patient’s body
and can be used to closely monitor the physiological
condition of patients. These medical sensors monitor the
patient’s vital body parameters, such as temperature,
heart rate, blood pressure, oxygen saturation, and transmit
the data to a doctor in real time [1]. When a doctor
reviews the transmitted sensor readings, they can get a
better understanding of a patient's health conditions. The
benefit for the patients is that they do not need to
frequently visit the hospital, thus patients could reap time
Manuscript received June 19, 2016; revised January 19, 2017.
and money savings. Such wireless medical sensors will
continue to play a central role in the future of modern
healthcare. People living in rural areas would especially
benefit, since 9% of physicians work in rural areas while
almost 20% of the US population lives there [2]-[6]. A
shortage of physicians and specialist is a big issue in such
areas, even today. But Wireless Medical Sensor Network
technology has the potential to alleviate the problem.
Many research related to change the material, or structure
is booming up [7]-[17].
II. BACKGROUN INTRODUCTION
A. Class AB PA Design
Figure 1. Block diagram of a typical sensor node.
In a wireless sensor network, as seen in the Fig. 1
below, each device is capable of monitoring, sensing,
and/or displaying information. A sensor node is capable
of gathering sensory information, processing it in some
manner, and communicating with other nodes in the
network.
Fig. 1 shows that the basic sensing node can collect the
physiological signals (e.g.: such as EEG, ECG, body
temperature, blood pressure, heart beat etc.), when
attached to a human body [3]. The processing unit
processes all the sensed signals, then sends out the data
based on communication protocols. All the processed
data will be transmitted through a wireless link to a
portable, personal base-station. Doctors can then obtain
all the patients’ data through the network.
The main challenge for such sensor node is the high
power consumption of portable devices. A solution to this
challenge is the integration of the portable devices’
digital and RF circuitry into one chip.
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©2017 Journal of Image and Graphicsdoi: 10.18178/joig.5.1.34-38
Figure 2. Block diagram of a transmitter
The receiver will receive the signal and will also
perform DSP processing after the data is sent out by the
transmitter [18]. Fig. 2 is the transmitter diagram. It is
desirable that the transmitter and receiver are low power
devices. The director-conversion transmitter is very
popular for such applications, because it offers versatility,
flexibility, spectral efficiency, and low complexity. These
features make the transmitter simpler than the super-
heterodyne transmitter. Small chip and circuit size, and
low power consumption can be achieved with a direct-
conversion transmitter architecture. For the front-end
transmitter, the major objectives are 1) transmit RF
signals and 2) recover the biosignal classification. This
paper proposes a low power receiver design. This paper is
mainly for the power amplifier design, since other
portions of the circuit design are already discussed in the
paper [18]. In order to meet the standards, the PA is
designed as shown in Table I.
TABLE I. PA DESIGN REQUIREMENT
Parameter Target
Output Power 18dBm
PAE 30%
Stability >1
S11 -10 dB
B. Class AB PA Design
Wireless Local Area Networks (WLANs) are
everywhere in our daily life, like air or water. During the
last 40 years, companies have been busy with
implemented WLAN infrastructures into offices to
provide more convenience and better data communication
across their LAN. For the sake of the interoperability,
most WLAN infrastructure use WLAN standards is
802.11a and primarily 802.11b [19]. The 802.11 standard
is used to provide solutions for business, home, and “hot
spot” WLAN needs [19].
The 802.11b standard was an expansion of the IEEE
802.11 standard. 802.11b can support bandwidths up to
11Mbps and uses the same radio signaling frequency (2.4
GHz) as 802.11. However, interference can incur from
appliances such as microwaves and cordless phones that
the same 2.4 GHz range [20]. The pros of the 802.11b
standard are lower costs and improved signal range. The
cons are slower maximum speed fewer simultaneous
users, and appliances can interfere with the frequency
band.
The 802.11a standard is another extension of the
original 802.11 standard. What many people do not know
is that 802.11a was created at the same time as 802.11b.
This is due to the fact that 802.11b is more popular than
the 802.11a. While 802.11b targets the home market,
802.11a standard is more suitable for the business market
because of its higher cost. The pros of the 802.11a are
faster speeds to support more users at the same time and
the use of specific frequencies which can prevent devices
from interfering with each other. The cons are higher cost,
a shorter range than 802.11b, and that it can be easily
blocked.
A new standard is 802.11g, which also has a speed of
54Mbps, similar to 802.11a. It is important to note that
802.11g is more attractive because it operates in the
lower 2.4GHz unlicensed radio band, while 802.11a
operates in the higher 5GHz unlicensed radio band. In
other words, compared to 802.11a, 802.11g throughput
drops slower over distance [21]. On the other hand,
sometimes the 802.11a standard is preferred, because the
5GHz band provides many more channels than 802.11g
[22].
With an 802.11g access point, 802.11b and 802.11g
network interface cards (NICs) can operate together. This
makes transition 802.11g smooth for existing 802.11b
networks because NICs can still work with the newer
802.11g access points [21].
Bluetooth is another wireless technology that has a
different purposes comparable to WLAN [22]. It is
designed to functioning in personal area networks (PANs)
where a few devices are carried by a person around their
desk [20]. The pros of bluetooth are its lower cost, lower
battery consumption, and the fact that it provides
application profiles, which are application-layer standards
that are designed to allow users to work together
spontaneously, with little intercession.
In contrast, the cons associated with bluetooth include
its rated speed, distance, number of devices, and
scalability. Bluetooth provides 722 kbps with a back
channel of 56 kbps which it may increase. However, it is
much slower than 802.11 standards. Also, its maximum
coverage is only 10 meters. Bluetooth scalability is poor
compared to 802.11, because 802.11 has more multiple
access points [19].
The problem that bluetooth has is that it can interfere
with 802.11b networks because they both operate in the
2.4GHz band. People are currently working to reduce
transmission interference between these two networks but
they still have some problems [19].
Many communication standards are widely used in our
current daily life in applications, such as cellular
networks, personal area networks (PAN), wireless local
area networks (WLAN), and the upcoming wireless
metropolitan area networks (WiMAX). These wireless
standards include Bluetooth, IEEE802.1 Ix, and Zigbee,
and are suitable for covering short distances at a low cost.
Using a receiver and transmitter in one Si chip is more
reasonable for maintaining low costs. Insufficient power
consumption is another concern for wireless devices
implementing these standards. The device’s low power
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can be achieved by the specific architecture, but this can
reduce its flexibility. Additionally, due to the limited
available bandwidth of the FCC, new standards for higher
data rates will require the use of non-constant envelope
modulation techniques which introduce even great power
consumption by the device [22].
III. PA DESIGN
Over the past 30 years, research on CMOS Radio-
Frequency (RF) front-end circuits has progressed
extremely quickly. The ultimate goal for the wireless
industry is to minimize the trade-offs between
performance and cost, and between performance and low
power consumption design [23].
Figure 3. Block diagram of a class AB power amplifier
The proposed Class AB amplifier has low output
power and good linearity based on the IEEE 802.11b
communication protocol. The class AB power amplifier
topology is shown in Fig. 3. The 2.4GHz PA is a two
stage common-source amplifier. The first stage is a driver
stage, used for providing sufficient driving capability and
a proper gain, as seen in Fig. 4(a) and the second stage is
the power output stage which used for performing
sufficient output power, as seen in Fig. 4(b) [24].
(a)
(b)
Figure 4. (a) Schematic of driver stage. (b) Schematic of output stage.
A. Class AB PA Design
To ensure low cost, so the PA is designed via a CMOS
process. And the initial requirements as seen in Table I.
For the drive-level circuit, the first design concern was
ensuring the input and output conjugate match to
different sizes of CMOS transistor. To get the optimum
bias, small-signal simulation and 1dB compression point
simulation are completed by their power output capability.
Resulting design values can be shown in Table II and
Table III.
TABLE II. PA DRIVER STAGE COMPONENT
Parameter Size (Unit)
Q1 W/L=0.6um/0.6um (f=56,m=16)
Q2 W/L=0.3um/0.6um (f=88,m=36)
Q3 W/L=0.3um/0.6um (f=2,m=6)
R1 14.5 Ohm
R2 10K Ohm
R3 80 Ohm
L1 36 nH(Q=20)
L2 15 nH (Q=20)
C1 240fF
C2 10 pF
C3 100pF
TABLE III. 2.4GHZ PA OUTPUT STAGE COMPONENT
Parameter Size (Unit)
Q4 W/L=0.3um/0.6um (f=66,m=24)
Q5 W/L=0.3um/0.6um (f=4,m=2)
R4 5 Ohm
R5 80 Ohm
L4 30 nH(Q=20)
L5 10 nH(Q=20)
L6 10 nH(Q=20)
L7 1 nH (Q=20)
C4 800 fF
C6 390 pF
C7 1.1 pF
Figure 5. Overall circuit schematic
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After the output stage and driver stage, the inter-stage
matching circuit is more challenging. If the input of
second stage and output of the first stage are all conjugate
matched to 50Ω, the two stages can be connected directly.
The complete optimized circuit is shown in Fig. 5.
B. Class AB PA Design Simulation
As seen in Fig. 6 (a), the output power is 8.5 dBm. As
seen in Fig. 6(b), the frequency is at 2.4 GHz the S11 is
less than -10 dB, also, the total power of the PA is 0.15
W.
As seen in Fig. 7(a), Kf is larger than 1 for all
frequencies from 1 to 3 GHz, so this circuit is totally
stable. And the PAE is 8.2% at input power 0 dB.
(a)
(b)
Figure 6. (a) PA output (b) S11
(a)
(b)
Figure 7. (a) Kf (b) PAE
IV. CONCLUSION
In hospital healthcare, the monitoring system can help
doctors to monitor the patient’s physiological parameters.
Using proposed technology, a pregnant woman can be
checked for such parameters as Blood Pressure (BP) and
heart rate of the woman and heart rate and movements of
fetal to control their health condition. In her proposed
system, a coordinator node can be attached to a patient’s
body to collect all the signals from the wireless sensors
and sends them to the base station. The attached sensors
on a patient’s body form a wireless body sensor network
and they are able to sense the heart rate, blood pressure
and so on. The main advantage of this system in
comparison to previous systems is to reduce the energy
consumption to prolong the network lifetime, speed up
and extend the communication coverage to increase the
freedom for enhance patient quality of life. Patients can
reduce the cost of staying hospital, and doctors can
monitor patients’ conditions at any time. Thus, poor
people can receive better healthcare, and do not have to
worry about money
This paper describes the method of designing and
simulating power amplifier using cadence software based
on SIMC CMOS process 180nm technology. This PA is
used for sensor networks. This research is still in the early
stages of development of a low cost and low power
device. In order to reach the performance that is needed,
the PA process uses group III and IV elements. This
circuit meets the scheduled requirements for the CMOS
process, but it still has room to improve performance
metrics. When the sensor is coupled with
communications technologies such as mobile phones and
the Internet, the sensor network constant information
flow between individuals and their doctors. Such low cost
and low power device can save a lot of hospitalization
resources. To realize this, future improvement is needed.
V. FUTURE WORK
This technologies are extremely important, because
they can detect and prevent illness without a patient ever
leaving their home. Thus, they could reduce hospital
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readmission rates, save hospital resources and save
patients money. Remote monitoring systems help patients
be aware of their physical conditions, and communicate
more efficiently with their physicians.
In order to build a complete transceiver, PA block is
not enough, as seen in the Fig. 2, and more blockers
should be done [18]. Also, more work can be done to
improve the performance, such as better PA topology. I
can cover and explore more deeply on this topic if time
permitted. I believe power consumption is very important
for healthcare applications. In order to achieve an ultra-
low power system, system and circuit design both need
improvements.
Secondly, since the technology nodes are becoming
smaller and smaller, technology creates more challenges
for analog/RF designers. For low supply voltage, it is not
easy to design a very linear mixer. Besides, accurate
device modeling is needed, due to the leakage and
process variations.
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Wei Cai is a graduate student at the
University of California, Irvine, CA. She
received her Masters degree from Dept. of Electrical Engineering, University of Hawaii
at Manoa and Bachelor degree from Zhejiang University, China. Her research interests
include device physics simulation, analog/ RF
circuit design.
Liang Huang is an associate Professor, Electronics College of Zhejiang Gongshang
University. He got PhD from Zhejiang University China, and finished his postdoc at
Polytechnic of Turin, Italy, and Hanyang
University, Seoul, Korea. His research is mainly focus on Research on: Intelligent
Control; Electrical Robotics.
Wujie Wen is an assistant Professor at Department of Electrical And University. He
got his Ph.D. in Electrical and Computer
Engineering from University of Pittsburgh in 2015, his research is in the span emerging
memory and next generation storage systems,
VLSI circuit design and computer architecture,
hardware acceleration (Neuromorphic
computing) and hardware security.
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AuPd@ MnO2 core-shell nanopillars for high-performance